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<h2><span class="refentrytitle">Class template old_ptr_if_copyable</span></h2>
<p>boost::contract::old_ptr_if_copyable — Old value pointer that does not require the pointed old value type to be copyable. </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../reference.html#header.boost.contract.old_hpp" title="Header &lt;boost/contract/old.hpp&gt;">boost/contract/old.hpp</a>&gt;

</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> T<span class="special">&gt;</span> 
<span class="keyword">class</span> <a class="link" href="old_ptr_if_copyable.html" title="Class template old_ptr_if_copyable">old_ptr_if_copyable</a> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <span class="identifier">T</span> <a name="boost.contract.old_ptr_if_copyable.element_type"></a><span class="identifier">element_type</span><span class="special">;</span>  <span class="comment">// Pointed old value type. </span>

  <span class="comment">// <a class="link" href="old_ptr_if_copyable.html#boost.contract.old_ptr_if_copyableconstruct-copy-destruct">construct/copy/destruct</a></span>
  <a class="link" href="old_ptr_if_copyable.html#idm45125847934656-bb"><span class="identifier">old_ptr_if_copyable</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  <a class="link" href="old_ptr_if_copyable.html#idm45125847934048-bb"><span class="identifier">old_ptr_if_copyable</span></a><span class="special">(</span><a class="link" href="old_ptr.html" title="Class template old_ptr">old_ptr</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>

  <span class="comment">// <a class="link" href="old_ptr_if_copyable.html#idm45125847949728-bb">public member functions</a></span>
  <span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">&amp;</span> <a class="link" href="old_ptr_if_copyable.html#idm45125847949168-bb"><span class="keyword">operator</span> <span class="special">*</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  <span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">*</span> <a class="link" href="old_ptr_if_copyable.html#idm45125847943568-bb"><span class="keyword">operator</span><span class="special">-&gt;</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  <span class="keyword">explicit</span> <a class="link" href="old_ptr_if_copyable.html#idm45125847937968-bb"><span class="keyword">operator</span> <span class="keyword">bool</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45885984391616"></a><h2>Description</h2>
<p>This pointer can be set to point to an actual old value copy using either  <code class="computeroutput"><a class="link" href="../../BOOST_CONTRACT_OLDOF.html" title="Macro BOOST_CONTRACT_OLDOF">BOOST_CONTRACT_OLDOF</a></code> or <code class="computeroutput"><a class="link" href="make_old_idm45125847890192.html" title="Function make_old">boost::contract::make_old</a></code>:</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span> <span class="comment">// Type `T` might or not be copyable.</span>
<span class="keyword">class</span> <span class="identifier">u</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
    <span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="special">...</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">virtual_</span><span class="special">*</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">{</span>
        <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr_if_copyable</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="identifier">old_var</span> <span class="special">=</span>
                <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">old_expr</span><span class="special">)</span><span class="special">;</span>
        <span class="special">...</span>
            <span class="keyword">if</span><span class="special">(</span><span class="identifier">old_var</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// Always null for non-copyable types.</span>
        <span class="special">...</span>
    <span class="special">}</span>

    <span class="special">...</span>
<span class="special">}</span><span class="special">;</span>
</pre>
<p><span class="bold"><strong>See Also:</strong></span></p>
<p> <a class="link" href="../../boost_contract/extras.html#boost_contract.extras.old_value_requirements__templates_" title="Old Value Requirements (Templates)">
        Old Value Requirements</a></p>
<p>
</p>
<p>

</p>
<div class="refsect2">
<a name="idm45885984351264"></a><h3>Template Parameters</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> T</pre>
<p>Type of the pointed old value. If this type is not copyable (i.e., <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&gt;::value</code> is <code class="computeroutput">false</code>), this pointer will always be null (but this library will not generate a compile-time error when this pointer is dereferenced). </p>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idm45885984346560"></a><h3>
<a name="boost.contract.old_ptr_if_copyableconstruct-copy-destruct"></a><code class="computeroutput">old_ptr_if_copyable</code> 
        public
       construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="idm45125847934656-bb"></a><span class="identifier">old_ptr_if_copyable</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>Construct this old value pointer as null. </li>
<li class="listitem">
<pre class="literallayout"><a name="idm45125847934048-bb"></a><span class="identifier">old_ptr_if_copyable</span><span class="special">(</span><a class="link" href="old_ptr.html" title="Class template old_ptr">old_ptr</a><span class="special">&lt;</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="special">&amp;</span> other<span class="special">)</span><span class="special">;</span></pre>Construct this old value pointer from an old value pointer that requires the old value type to be copyable. <p>Ownership of the pointed value object is transferred to this pointer. This constructor is implicitly called by this library when assigning an object of this type using <code class="computeroutput"><code class="computeroutput"><a class="link" href="../../BOOST_CONTRACT_OLDOF.html" title="Macro BOOST_CONTRACT_OLDOF">BOOST_CONTRACT_OLDOF</a></code></code> (this constructor is usually not explicitly called by user code).</p>
<p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><code class="computeroutput">other</code></span></p></td>
<td><p>Old value pointer that requires the old value type to be copyable. </p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="idm45885984327088"></a><h3>
<a name="idm45125847949728-bb"></a><code class="computeroutput">old_ptr_if_copyable</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">&amp;</span> <a name="idm45125847949168-bb"></a><span class="keyword">operator</span> <span class="special">*</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Dereference this old value pointer. <p>This will generate a run-time error if this pointer is null, but no compile-time error is generated if the pointed type <code class="computeroutput">T</code> is not copyable (i.e., if <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&gt;::value</code> is <code class="computeroutput">false</code>).</p>
<p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>The pointed old value. Contract assertions should not change the state of the program so this member function is <code class="computeroutput">const</code> and it returns the old value as a reference to a constant object (see  <a class="link" href="../../boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.constant_correctness" title="Constant-Correctness">
        Constant Correctness</a>). </p></td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="identifier">T</span> <span class="keyword">const</span>  <span class="special">*</span> <a name="idm45125847943568-bb"></a><span class="keyword">operator</span><span class="special">-&gt;</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Structure-dereference this old value pointer. <p>This will return null but will not generate a compile-time error if the pointed type <code class="computeroutput">T</code> is not copyable (i.e., if <code class="computeroutput">boost::contract::is_old_value_copyable&lt;T&gt;::value</code> is <code class="computeroutput">false</code>).</p>
<p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>A pointer to the old value (null if this old value pointer is null). Contract assertions should not change the state of the program so this member function is <code class="computeroutput">const</code> and it returns the old value as a pointer to a constant object (see  <a class="link" href="../../boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.constant_correctness" title="Constant-Correctness">
        Constant Correctness</a>). </p></td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">explicit</span> <a name="idm45125847937968-bb"></a><span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Query if this old value pointer is null or not (safe-bool operator). <p>(This is implemented using safe-bool emulation on compilers that do not support C++11 explicit type conversion operators.)</p>
<p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>True if this pointer is not null, false otherwise. </p></td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2008-2019 Lorenzo Caminiti<p>
        Distributed under the Boost Software License, Version 1.0 (see accompanying
        file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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